In the first chapter of the book, Piggy notices the conch shell in the water. He suggests to Ralph how it might be used. When you make a hole in it and blow it correctly, it makes a loud sound. So Piggy suggests that Ralph can use it to let everyone know that there are other survivors (at first no one knows who has survived the crash). Later on in the story, the conch is used for calling meetings and for designating whose turn it is to talk.
The conch, in a way, symbolizes civilization. It is the symbol of the kids' impulse to try to have rules and run their lives in a civilized way. This is why it is a big deal later on when the conch is destroyed.
The conch in the novel 'Lord of the Flies' by William Golding is a beautiful and mysterious object. It may well be a novel sight for the boys and seems to demand attention and respect by its very beauty. The conch gets noticed - and would get noticed anywhere. So, it follows that anyone holding the conch would get noticed too and thus it seems to confer a myustical sort of authority. In other words, anyone holding the conch (particularly if he had a 'natural presence' of leadership already) would command respect. So the boys fight over the conch and who should hold it and who should be leader. Look out for who gives respect to the conch and who does not. It becomes a sort of 'mouthpiece' or symbol, a bit like 'The Mace' in the English Parliament.
In the book "The Lord of the Flies" the conch is a representation of civilization. When a boy wants to speak he is supposed to hold the conch.
The conch was originally found by Ralph and Piggy. Since Ralph was the first to use the conch and the others had gathered together in response, the group chooses Ralph to be their first leader.
Ralph being appointed as the leader instead of Jack creates the first evidence of conflict. Jack believes he should serve as the leader.
Later Jack destroys the conch. Thereby, making the statement that Ralph's reign as leader is completely over.